This invention relates to an automatic tool changer in a machine tool, and more particularly, to the automatic tool changer capable of shortening times required for mounting or dismounting a tool holder of the machine tool in which a spindle head is reciprocatingly mounted to a main frame, and a tool magazine accommodating a plurality of grippers for holding the tool holders is rotatably arranged, whereby the tool holders are automatically transferred between the spindle head and the tool magazine in accordance with the reciprocating motion of the spindle head.
There is known a multifunctional machine tool represented, for example, by a machining center (MC) having a construction capable of carrying out various machining works such as thread cutting and drilling works to a workpiece by using a single machine. In the machine tool of this type, a plurality of tools such as tapping tool or drilling tool are provisionally accommodated in predetermined portions of the tool magazine, and an automatic tool changer (ATC) is generally arranged for selecting one of the desired tools in the tool magazine as occasion demands, which is then automatically changed by a used tool mounted in the spindle head. Although various types of the automatic tool changer have been provided in the conventional art of this field, in one practical example, the spindle head is moved in a vertical direction (hereinafter called Z-axis direction) and tools are changed between the spindle head and the tool magazine arranged to be movable in a vertical direction with respect to the spindle head through an operation of a cam mechanism.
For example, the machine tool disclosed in the Japanese Patent Laid-open (KOKAI) Publication No. 60-155338 includes a spindle head provided movably in the Z-axis direction and a rotationally indexable tool magazine provided on a frame of the machine tool to be movable therealong in a vertical direction independently of the movement of the spindle head. According to this construction, when the spindle head moves to a first return direction, a gripper assembled in the tool magazine firmly grips a tool mounted to a tip end of the spindle. The gripped tool is released from the main spindle by a second return movement of the spindle head. Then, the tool is completely separated from the spindle head by a third return movement of the spindle head. The tool magazine is then rotationally index the tool, and thereafter, the spindle head is operated at three times in the manner reverse to that referred to above, thus performing a series of tool charging operation.
According to the automatic tool changer described above, the tool magazine is parallelly moved with respect to the movement of the spindle head in the Z-axis direction during the time ranging between the starting and finishing of the tool changing operations for transferring the tool holder from the spindle head to the tool magazine and for transferring the tool holder from the tool magazine to the spindle head.
According to the automatic tool changer in which the spindle head is reciprocated in the Z-axis direction and the tool magazine is moved parallelly to, but independently from, the movement of the spindle head to carry out the interchange of the tools between the moving spindle head and the moving tool magazine, the tool magazine is vertically moved in its entirety during the tool changing operation. The tool magazine is however equipped with a plurality of grippers in radial arrangement each detachably holding the tool holder. The weight of the entire tool magazine is thus considerably heavy. Therefore, large inertia moment will occur due to the self-weight of the tool magazine when the tool magazine is moved vertically at high speed for the quick transfer of the tools. Accordingly, a considerably large mechanical shock will be imparted at a time when the spindle abuts the gripper through the tool holder.
In order to alleviate such mechanical shock, in a conventional technique, the moving speed of the spindle head in the Z-axis direction is decreased to surpress the inertia moment caused by the mass of the tool magazine. However, the decrease in moving speed of the spindle head for the purpose of alleviating the mechanical shock, in spite of the fact that the spindle head inherently has a capacity of moving at a sufficiently high speed, requires inevitable unnecessary time for changing the tool. This fact constitutes a counter tendency to the present situation at which frequent tool changing operations are required with possibly shortened tool changing time for producing reduced numbers of productions yet having various kinds.
There are related inventions described in U.S. Pat. No. 4,679,296, Japanese Patent Publication No. 58-24220 and copending U.S. patent application Ser. No. 8,654 filed on Jan. 30, 1987.